The present invention relates generally to the vertical deflection system of an oscilloscope, and more particularly to a method and system for automatically calibrating the vertical system.
It is well established that oscilloscopes are electrical measurement tools which graphically display electrical events upon a viewing screen wherein the vertical axis thereof represents the magnitude or amplitude scale of the electrical events while the horizontal axis thereof represents the time scale. Typically, the oscilloscope viewing screen has superimposed thereon a grid of precisely spaced vertical and horizontal lines, such grid being known in the art as a graticule, to permit an operator to measure the electrical event, or input signal, with some degree of accuracy. Of course, to ensure this accuracy, the vertical and horizontal deflection systems must be calibrated in order to scale any electrical input signal to the graticule grid divisions.
The vertical deflection system may typically include two or more vertical input channels which are selectively connected to a vertical deflection amplifier to be applied to the vertical deflection plates of a cathode-ray tube (CRT). Each vertical channel typically includes a wide range of selectable gain factors to accomodate a variety of signal amplitudes, and these gain factors, known in the art as vertical deflection factors, may be provided in steps in a 1-2-5 sequence. Calibrating the vertical deflection system in the past has involved a technician manually adjusting variable circuit elements while viewing the display to provide the correct deflection of an externally-applied standard reference signal of known amplitude. This is typically time consuming because the calibration procedure must be carried out for each vertical input channel and for each deflection factor, and is accurate only to the degree of accuracy of the reference input signal and the visual perception of the technician. To cut down on the number of adjustments required, matched attenuators and appropriatelyscaled amplifier gain-setting elements have been used for a certain number of deflection factors. To facilitate the accuracy of amplitude measurement, delta voltage cursors have been added wherein the difference between a first and second adjustable amplitude marker may be read out alphanumerically. However, the calibrating technician must manually adjust the relative vertical deflection of the cursors to match the normalized (calibrated to a nominal standard reference) deflection factors.